Algorithm development for dynamic optimization of heat exchanger network cleaning using continuous time formulation approach

Heat exchanger is important and employed in most stages of industrial processing. The main problem of heat exchanger is fouling on the heat transfer surfaces. The fouling causes the retardation of heat transfer efficiency with time. This is the reason for the loss in energy and the increment of operation cost. Therefore, the cleaning of fouled units is important in order to restore their hydrothermal performance. In this work, the simulations of heat exchanger in a case of single unit and also in network heat exchanger are performed based on linear and asymptotic fouling models. The effect of variation with time of fouling rate, overall heat transfer coefficient, temperatures of hot and cold streams, and heat transfer rate are studied. Besides this, we developed a new technique to formulate the optimization problem of optimal cleaning time schedule of heat exchanger cleaning using continuous time approach. In this approach, the number of cleaning operation is predicted priorly, and the time period between each cleaning operation is then determined. The objective function of this problem is the minimizing of overall operating cost. The results obtained from this technique are better than the results obtained using the discrete time approach.换热器（Heat Exchanger）广泛应用于工业加工的多数环节，是至关重要的核心设备。其面临的主要问题为传热表面结垢（Fouling）：结垢会随时间推移逐步降低传热效率，进而引发能量损失与运行成本攀升。因此，对结垢设备开展清洗作业以恢复其水热性能，具备重要的工程意义。本研究基于线性与渐近结垢模型，分别开展了单台换热器及换热器网络的模拟分析，系统研究了结垢速率、总传热系数、冷热流体温度以及传热速率随时间的变化规律。此外，本研究提出了一种全新的方法，采用连续时间法构建换热器最优清洗时间计划的优化问题：该方法可预先预测清洗操作的总次数，并确定相邻两次清洗之间的时间间隔，该优化问题的目标为最小化总运行成本。研究结果表明，该方法所得优化结果优于离散时间法的结果。